Stabilized photographic silver halide emulsions



I STABILIZED PHOTOGRAPHIC SILVER HALIDE EMULSIONS,

N Drawing- Application April 29, 1954,

Serial No. 426,547 I 12 Claims. o1. 95-4 This invention relates to fog-inhibiting agents and stabilizers for photographic emulsions and to photographic emulsions containing them.

" 'This application is a continuation-in-part of our application Serial No. 365,542, filed July 1, 1953, now Patent No. 2,713,541

' It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog where it is necessaryto distinguish between it and the efiects of accidental exposure to radiation; in this invention, we are not concerned with'the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increaseswith the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photo'- graphic emulsions by storage at increased temperature or humidity, or both. It is, of course, desirable to have emulsions as stable aspossible under the conditions of high temperature and humidity which may occur in. tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While'antifoggants and stabilizers may protect, to some exetnt, against such effects, it is normally understood that an 'antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development tomaxirnum contrast and speed, or both. Y v 1 It is, accordingly, an object of our invention to provide a methodfor stabilizing photographic emulsions. Afurther object of our invention is to maintain the sensitivity and fog of silver halide emulsions at or close to initial optimum values underkeeping conditions of high temperature and humidity. A further object is to provide photographic silver halide emulsions containing antifoggants or stabilizers. Other objects will become'apparent from a consideration of the following description and examples.

The above objects are, in general, accomplished by adding to the photographic emulsion certain organic compounds of the following general formula:

wherein R1 represents a hydroxyl group, a mercapto group, an alkylmercapto group (e. g. methylmercapto, ethylmercapto, carboxymethylmercapto, etc.), an alkyl group (e. g. methyl, ethyl, n-propyl, n-butyl, isobutyl, etc.), or a hydrogen atom and R2 represents a hydroxyl group, a mercapto group, an alkylmercapto group (e. g. methylmercapto, ethylmercapto, carboxymethylmercapto, etc.), an amino group (e. g. amino, methylamino, ethylamino, n-propylamino, dimethylamino, diethylamino-din-propylamino, etc.), an alkyl group (e. g. methyl, ethyl, n-propyl, n-butyl, isobutyl, etc.), or a hydrogen atom, but at least R1 or R2 represents a hydroxyl group (OH) or a mercapto group (SH). Compounds represented by the above formula wherein R1 and/or R2 are a hydroxyl group have been found to be particularly useful. In general, the compounds represented by the above formula can be prepared according to the method described in U. S. Patent 2,407,204, issued September 3, 1946. See also Parker and Webb U. S. Patent 2,543,333, issued February 27, 1951.

The fog inhibitors which we propose to use are added to the emulsion during the process of manufacture, to

avoid loss of sensitivity and to inhibit the growth of fog with passage of time under non-ideal conditions of storage.

A solution of the compounds of the invention when added in suitable concentration, before coating, to unsensitized, chemically sensitized, or optically sensitized photographic emulsions does not appreciably afiect the sensitometric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are made at appreciable intervals of time, at elevated temperatures and dry or somewhat humid conditions, these compounds do stabilize photographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations: '(1) the emulsific'ation and digestion or ripening of the silver halide, (2) the freeing of the emulsion from excess soluble salts, usually by washing, and (3) the second digestion or after-ripening to obtain increased senstivity. (Mees The Theory of the Photographic Process, 1942.) We prefer to add the foginhibiting agents after the final digestion or after-ripening,

although they can advantageously be added prior to digestion.

Listed below are a number of compounds coming within the scope of the above general formula, which we have found to be particularly advantageous in practicing our invention. These compounds belong to a group of compounds which we shall designate as pentazaindenes.

7-hydroxy-5-methyl-1,2,3,4,G -pentazaindene 7-hydroxy-1,2,3,4,6-pentazaindene 7 -11ydroxy-5-n1ercapto-1,2,3,4,6-pentazaindeue T-amiu5-carboxymcthylmercapto-l,2,3,4,0-pentazaindeue N N k N-H N N 7-n1ercapto-1,2,3,4,6-pentazaindcne N N K \N/ 5,7-dimercapto-1,2,3 ,4,G'pentazaindene -ethylmercaptoJ-hydroxy-l,2,3,-l,6-pentazaindene N g \N/ a-llydroxy-l,2,3,4,6-pentazalndcue 5-l1ydroxy-7-methyl-12,3,4,G-pentazalmlenc The photographic emulsions used in practicing our invention are generally of the developing-out type; also, it is to be understood that photographic emulsions of varying halide content can advantageously be used. The antifoggant compounds used in our invention have been found particularly useful when employed in conjunction with gelatino-silver bromiodide emulsions, although they can also be advantageously employed for stabilizing othersilver halide emulsions, such as gelatino-silver chloride, bromide, chlorobromide, chlorobromiodide, etc.

The emulsions can also be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U. S. Patent 1,574,944 and U. S. 1,623,499, and Sheppard and Brigham U. S. Patent 2,410,689.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium and platinum, all of which belong to group VIII of the periodic table of elements and have an atomic weight greater than 100. Representative compounds are ammonium chloropalladate, potassium chloroplatinate and sodium chloropalladite, which are used for sensitizing. in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U. S. Patent 2,448,060, and as antifoggants in higher amounts, as described in Trivelli and Smith U. S. Patents 2,566,245 and The emulsions can also be chemically sensitized with gold salts as described in Waller and Dodd U. S. Patent 2,399,083, or stabilized with gold salts as described in Damschroder U. S. Patent 2,597,856 and Yutzy and Leermakers U. S. Patent 2,597,915. Suitable compounds are potassium chloroaurite, potassium aurithiocyanatqpotassium chloroaurate, auric trichloride and Z-aurosulfobenzw thiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U. S. Patent 2,487,850), polyamines such as diethylene triamine (Lowe and Jones U. S. Patent 2,518,698), polyamines such as spermine (Lowe and Allen U. S. Patent 2,521,925), or bis-(p-arninoethyl) sulfide and its watersoluble salts (Lowe and Jones U. S. Patent 2,521,926).

The emulsions can also be stabilized with the mercury compounds of Allen, Byers and Murray U. S. application Serial No. 319,611 (now U. S. Patent 2,728,663, issued December 27, 1955), Carroll and Murray U. S. application Serial No. 319,612 (now U. S. Patent 2,728,664, issued December 27, 1955) and Leubner and Murray U. S. application Serial No. 319,613 (now U. S. Patent 2,728,665, issued December 27, 1955), all filed November 8, 1952.

The stabilizing combinations of pentazaindenes are efiective in the presence or absence of optical sensitizing dyes. Since optical sensitizing may afiect stability of emulsions with respect to sensitivity, fog and latent image changes, the action of the compounds of this invention is not completely independent of optical sensitizing or other emulsion variables. We have found, howeventhat both nnsensitized emulsions and emulsions sensitized with cyanine or merocyanine dyes or both can be treated with pentazaindenes according to our invention.

The antifoggant and stabilizing action was determined by incubation of the emulsions for one week at a temperature of F. and constant relative humidity (obtained by placing the emulsions in closed containers, the ambient temperature being 70 F. and relative humidity 55% prior to sealing the containers). The etficiency of the various antifoggants was determined by measuring the speed, gamma and fog of the incubated emulsions containing an antifoggant and comparing these measurements with those of the same batch of emulsion before incubation. Alsosimilar measurements were made on a-photographic emulsion containing no antifog ant, both before and aiter incubation. The tests were made using a high speed silver, bromiodidc emulsion exposed on an Eastman Type lb sensitometer and developed for 5 minutes in a developer of the following composition:

Grams N-methyl p-aminophenol sulfate 2.5 Hydroquinone 2.5 Sodium sulfite (desiccated) 30 Sodium metaborate 10 Potassium bromide 0.5

Water to 1 liter Anmog Fresh Test Incubation Test gent g./mol Agxw 1 F 10 1 F pound speed 7 0g speed 7 In a manner similar to that illustrated in the above example, other pentazaindenes selected from those represented by the above general formula can be incorporated in photographic emulsions for the'purpose of stabilization. The fog-inhibiting agents useful in practicing our invention can be used in various kinds of photographic emulsions. In addition to being useful in'ordinary nonsensitized emulsions, they can also be used in orthochromatic, panchromatic and X-ray emulsions. If used with sensitizing dyes, they can be added to the emulsion before or after the dyes are added. Suitable dispersing.

agents for the silver halide emulsions stabilized according to our invention "comprise gelatin, o'r'other colloids, such as collodion, albumen, cellulose organic derivatives, synthetic resins, etc.

The optimum amount of fog-inhibiting agent can be determined by making the customary tests employed in 2,407,204, however, the following examples will serve to illustrate further this method. I Example A.-7-hydr0.1cy-5-methyl-1,2,3,4,6-

' pentazainden'e To a solutionof 37 g. (0.39 mol.) of acetarnidine hydrochloride in 150 cc; of absolute ethanol was added 45 g. (0.39'mo1.) of ethyl cyanoacetate.. A solution of 20 g. (0.87 mol.) of sodium in 300 cc. of absolute ethanol was prepared and the above solution added. The mixture was heated at reflux for 3 hours and the alcohol removed under vacuum. The, solid residue was dissolved in water, the solution filtered, and the filtrate acidified 1 with acetic acid. The solid was collected and recrystallized from water to give 48 g. (97%) of 4-an1ino-6-hy- I droxy-2-methylpyrimidine.

To a suspension of 17 g. (0.136 mol.) of 4-arnino-6- hydroXy-2-methylpyrimidine in 150 ml. of water was added 9.5 g. of sodium nitrite. The mixture was stirred emulsion making. Of course, theoptimum amount for a given emulsion will vary depending on the presence of emulsionaddenda, such as chemical .sensitizers, optical sensitizers, etc. In general, we have found that from 0.001 to 5.0 g. of fog-inhibiting agent per mole of silver halide is sulficient for the purposes of our invention. Those compounds which contain a mercapto (SH) group can advantageously be employed at concentrations of 0.001 to 0.1 g. per mole of silver halide, while those compounds which contain a hydroxyl (OH) group but no mercapto (SH) group can be employed at concentrations of 0.l to 5.0 g. per mole of silver halide.

*Ins'teadof adding the fog-inhibiting agent directly to the photographic emulsion, it is sometimes desirable to incorporate the fog-inhibiting agent in a separate layer which is placed in contact with the silver halide emulsion layer which is to be stabilized. Under such conditions, of course, it is advisable to use a higher concentration of fog-inhibiting agent than indicated above.

The compounds represented by the above general formula can alternatively be written in the following form-5 7 and 15 ml. of 9.5 N sulfuric acid added and the stirring continued for an additional hour. The blue green nitroso compound was collected and; dried (15 g.).

A suspension of 15 g. (0.0874 mol.) of the nitrosopyrimidine was prepared by stirring in 500 ml. of water. To this, 42g. (02 mol.) ofsodium'hydrosulfite was added. The mixture was boiled for 2 minutes. and then cooled. The white solid was collected and suspended in 150 ml. of water while 30 ml. of concentrated sulfuric acid was added. The mixture was diluted with ml. of water and heated. The resulting solution was filtered and the filtrate cooled, whereby 13 g. of the 4,5-diamino- 6 hydroxy-Z-methylpyrimidine sulfate separated. A solution of 7 g. (0.0295 mol.) of the diamine and 5 g. of sodium nitrite in 50 mlof 1N sodium hydroxide was prepared. The solution was acidified by the gradual addition of acetic acid. After heating on the steam bath for 30 minutes and cooling in an ice bath, the white solid that had separated was collected. Recrystallization from Water gave 5.5 g. of the 5-methyl-7-hydroxyl,2,3,4,6-pentaz aindene.

Analysis. Calcd. for C5H5N5OJ/2HNOs-l- /2H2O: C=34.2; H= 3.7; N=43. Found: C=33.9; H=4.3; N=43.

v Example B.7-amin0-5-carb0xymethylmercapto- 1,2,3,4,6-pentazairrdene I 1,2,3,4,6-pentazaindene.

What we claim as our invention and desire secured by Letters Patent of the United States is:

l. A photographic silver halide emulsion containing a compound selected from the group consisting of a con1- pound represented by the following formula:

and a compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group.

consisting of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms, and R2 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH), an alkylmercapto group, an amino group, and an alkyl group containing from 1 to 4 carbon atoms, but at least one of the groups selected from R1 and R2 is a member selected from the group consisting of a hydroxyl group (OH) and a mercapto group (SH).

2. A photographic silver bromiodide emulsion containing a compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl' group (OH), a mercapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms, and R2 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH), an alkylmercapto group, an amino group, and an alkyl group containing from 1 to 4 carbon atoms, but at least one of the groups selectedfrom R1 and R2 is a member selected from the group consisting of a hydroxyl group (OH) and a mercapto group (SH).

3. A photographic silver halide emulsion containing a compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms, and R2 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), a, mercapto group (SH), an alkylmercapto group, an amino group, and an alkyl group containing from 1 to 4 carbon atoms, but at least one of the groups selected from R1 and R2 is. a hydroxyl group (OH).

4. A photographic silver halide emulsion containing a compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), 21 mercapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms, and R2 represents a member selected from the group consisting compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms.

6. A photographic silver bromiodide emulsion containing a compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms.

7. A photographic silver halide emulsion containing a compound having the following formula:

8. A photographic silver halide emulsion containing a compound having the following formula:

9. A photographic silver halide emulsion containing a compound having the following formula:

10. A photographic siliver halide emulsion containing a compound having the following formula:

NH nooc-onfs- \N 12. A light-sensitive photographic element comprising a silver halide emulsion layer and an organic colloid. layer contiguous to saidemulsion layer, at least oneof said layers containingas astabilizing agent for said emulsion layer a compound selected from those represented by the following general formula:

wherein R1 represents a member selected from the group consisting of a hydrogen atom, a hydroxyl group (OH), :1 mcrcapto group (SH), an alkylmercapto group, and an alkyl group containing from 1 to 4 carbon atoms, and R2 represents a member selected from the group consisting 10 of a hydrogen atom, a hydroxyl group (OH), a mercapto group (SH) {an alkylmercapto group, an amino group, and an alkyl group containing from 1 to 4 carbon atoms, but at least one of the groups selected from R1 and R2 is a member selected from the group consisting of a hydroxyl group (OH) and a mercapto group (SH).

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF A COMPOUND REPRESENTED BY THE FOLLOWING FORMULA: 